Conventionally, the method of sampling industrial reaction vessels such as fermentors, involves the aseptic and manual removal of individual aliquots through a sample port connected to the vessel into a receiver most commonly a test tube or a flask. As it is essential to obtain representative samples, heterogeneous material must be taken directly from the stirring reaction mixture for sampling. The heterogeneous material which is difficult to filter either due to high viscosity or complexity of constituents of different sizes and textures, usually can only be removed efficiently by the manual method. A notorious example is fermentation broths with unusually high percent solids which are routinely removed aseptically and manually into a receiver protected from contamination only by a cotton plug. The individual samples are subsequently measured, filtered/centrifuged and stored until required analysis can be performed.
The conventional method is inherently unsatisfactory because (1) replacement of receivers for obtaining consecutive samples for analysis is a high contamination risk; (2) the necessary delay incurred during the course of the conventional method, i.e., the time-consuming manual removal, separate filtration, storage prior to analysis, and subsequent manual dilution of samples, are sources of inaccuracy. The delayed analysis may not correspond to the course of the fermentation in real time, and the overly manipulated samples may not give the true analysis of the fermentation due to contamination or decomposition; and (3) total on-line automation and control of the process is impossible with manual sampling.
Automation of an industrial fermentation process highly economize the production by avoiding "over-fermentation". It saves time and energy. It also eliminates the risk of "spoiling" the fermentation where sensitive products are involved and may decompose if the fermentation is not terminated timely.
Most semi-automated biochemical processes, for example, a fermentation process, involve an off-line autoanalyzer which analyzes samples while monitoring the progress of the reaction. However, samples continuously taken from the reaction mixture for sampling must be properly filtered or centrifuged and diluted before entering the autoanalyzer in order to bring the concentrations of analyzed components within the range of the STDS and to avoid clogging of the instrument.
It is well-known how difficult it can be when one attempts to conduct a continuous and efficient filtration of a viscous heterogeneous reaction mixture, especially when it involves high solids containing media and the fermentation lasts for days. Thus, even though some commercially available high-efficiency radial flow-cells have been used for filtering solutions containing extracts or casein from dairy products, no attempts of direct, aseptic, and continuous filtration of a whole fermentation broth has been fully successful.
Accordingly, it is an object of the present invention to provide for an improved flow cell capable of continuous and aseptic filtration for a relatively long period of time a reaction mixture of similar viscosity and complexity of texture as a typical fermentation broth.
Another object of the present invention is to utilize the improved flow cell in a method for automatically monitoring the progress of a reaction which involves (1) filtering a continuous flow of the reaction mixture during the entire reaction period; (2) periodically removing discreet samples from the continuously flowing filtrate stream and feeding them to analyzers in order to monitor the progress of the reaction; (3) returning to the reaction vessel the residue which is swept off from the surface of a biological membrane by a recirculating radial flow of the process stream; and (4) returning to the reaction vessel the unused sterile filtrate.
For example, the present invention could be used to incorporate the automatic monitoring method into a computer-controlled system for the automation of the reaction or the fermentation process.